1. Field of the Invention
This invention relates to a headlamp unit for a vehicle such as an automobile, and more particularly to the structure of an actuator for deflecting an optical axis of a headlamp used in a headlamp unit that has luminous distribution control means (for example, but not by way of limitation, an adaptive front-lighting system (hereinafter referred to as “AFS”)) for changing the direction and range of illumination by the headlamp, in accordance with a running condition.
This invention further relates to a brushless motor in the above actuator, and more particularly to a brushless motor with a reduced number of component parts, and which can be easily assembled, thereby achieving a low-cost and lightweight design.
2. Background of the Related Art
In a proposed related art AFS illustrated in FIG. 1, to enhance a running safety of an automobile, information representative of a running condition of an automobile CAR is detected by sensors 1, and detection outputs of these sensors 1 are sent to an electronic control unit (hereinafter referred to as “ECU”) 2. For example, the sensors 1 include a steering sensor 1A for detecting a steering angle of a steering wheel SW of the automobile CAR, a speed sensor 1B for detecting the speed of the automobile CAR, and leveling sensors 1C (for simplicity, only the sensor for a rear axle is shown) for respectively detecting the heights (or levels) of the front and rear axles so as to detect a horizontal condition (leveling) of the automobile CAR. These sensors 1A, 1B and 1C are connected to the ECU 2.
In accordance with the outputs of the sensors 1 inputted thereto, the ECU 2 controls swivel lamps 3R and 3L (that is, headlamps 3 each capable of deflecting an illuminating direction right and left to change its luminous distribution characteristics) provided respectively at right and left portions of the front of the automobile.
In one related art example of the swivel lamp 3R, 3L, a reflector and a projector lamp are provided within the headlamp, and can be angularly moved horizontally. These lamps 3R, 3L are driven for rotation by a drive power source (such as a drive motor) through rotation drive means. Here, a mechanism, including this rotation drive source, is referred to as an actuator. When a car travels along a curved road, this kind of AFS enables the headlamps to illuminate a road ahead of the curve in accordance with the running speed of the car, and therefore the AFS is effective in enhancing the running safety of the car.
In another related art proposal, an actuator is provided in which a drive motor serving as a drive power source and a gear mechanism serving as rotation drive means are mounted within a casing. Also provided is a circuit means (for controlling the rotation of the drive motor) within the above casing. In such an actuator, to achieve a lightweight and low-cost casing design and enhance the ability of mounting the casing within the lamp and enhance the reliability of the operation of the gear mechanism mounted within the casing, a relatively inexpensive glass fiber-containing PBT resin, which has high flexural rigidity and good heat resistance, is used as a material for forming the casing.
Although a plurality of gears, forming the gear mechanism mounted within the casing, are usually made of a metal material, the related art scheme forms these gears by a resin material to achieve the lightweight design and low-cost design of the actuator. In this case, a thermosetting resin, such as a phenolic resin that can be highly precisely molded, or a resin such as a polyacetal resin, is used. Grease is coated on the gears to provide lubricitation between the adjacent gears.
In such a related art actuator, a brushless motor is used as the drive motor. The brushless motor is not provided with a so-called commutator formed by brushes and a moving contact, and is advantageous in that it can be formed into a compact and lightweight construction. Such a brushless motor is used, for example, as a drive source of a rotation drive device for deflecting an optical axis of a vehicle lamp described in JP-A-2002-160581 (Japanese Patent Application Publication Number: 2002-160581, the contents of which is incorporated herein by reference).
More specifically, FIG. 20 shows a related art cross-sectional view of an outer rotor-type brushless motor. Identical reference numerals in this Figure and other Figures of preferred embodiments (described later) of the invention denote corresponding portions. A thrust bearing 421 and a sleeve bearing 422 are fitted in a hollow boss 414 formed on an equipment housing 41, and a rotation shaft 423 is rotatably inserted in this sleeve bearing 422. A stator coil 424 is fixedly mounted on the hollow boss 414, and is disposed above a printed circuit board 45 provided within the housing 41. A cylindrical container-like rotor 426 is mounted on the rotation shaft 423, and is rotatably disposed around the stator coil 424. In the stator coil 424, a plurality of coils 4243 are wound on a petal-shaped core 4241 such that the coils 4243 are arranged in a circumferential direction to produce a plurality of magnetic poles in the circumferential direction.
The core 4241 is fitted at its central hole 4244 on the outer periphery of the hollow boss 414, and therefore is supported by this hollow boss 414. Terminals 4243a of the coils 4243 are electrically connected to the printed circuit board 45, and an alternating current, for example, a three-phase alternating current, is supplied to these coils through the printed circuit board 45.
In the rotor 426, an annular rotor magnet 428 is mounted within a cylindrical container-like metal yoke 427, as shown in FIG. 21, which is an exploded, cross-sectional view. A plurality of S-poles and N-poles are alternately magnetized in the rotor magnetic 428 in a circumferential direction. The rotation shaft 423 is integrally connected to the yoke 427 through a bushing 4272 fitted in a central hole 4271 in this yoke. A gear 441 for transmitting a rotational force to the exterior is fixedly mounted on a distal end portion of the rotation shaft 423.
In this brushless motor, when a three-phase current is supplied to the stator coil 424, S-poles and N-poles are alternately produced at a plurality of portions of the core 4241 of the stator coil 424 in the circumferential direction. Therefore, a magnetic force produced between this stator core and the circumferentially-arranged S-poles and N-poles of the rotor magnet 428 changes based on the phase of the three-phase current. The rotor magnet 428 and the yoke 427, integrally connected thereto, are rotated by this magnetic force. When the yoke 427 thus rotates, the rotation shaft 423 rotates together with this yoke. As a result, the gear 441, fixedly mounted on the distal end portion of this rotation shaft, is rotated. In the brushless motor, the stator coil 424 for supplying electric power is fixed, and therefore, there is no need to provide a commutator for changing the direction of a current flowing through the coils. This related art design is advantageous in achieving a compact and lightweight design of the motor.
For assembling the related art brushless motor, the stator coil 424, having the coils 4243 wound on the core 4241, is mounted on a predetermined portion of the printed circuit board 45. Then, the terminals 4243a of the coils 4243 are connected to electrodes on the printed circuit board 45 by soldering or the like, and the stator coil 424 is supported above the printed circuit board 45 in a floating condition. Then, the printed circuit board 45 is mounted within the housing 41. At this time, the stator coil 424 is fitted on the outer periphery of the hollow boss 414 of the housing 41.
On the other hand, in the rotor 426, the bushing 4272 is fitted into the central hole 4271 of the yoke 427 having the rotor magnet 428 mounted therein, and then the yoke is press-fitted on the rotation shaft 423 through the bushing 4272, and is fixed to the rotation shaft 424. Then the gear 441 is press-fitted on the distal end portion of the rotation shaft 423. Then, the thrust bearing 421 and the sleeve bearing 422 are fitted into the hollow boss 414 from the upper side of the printed circuit board 45, and also the proximal end portion of the rotation shaft 423 is inserted into the sleeve bearing 422, so that the rotation shaft 423 is borne by these bearings. As a result, the rotor 426 is mounted in a manner to cover the stator coil 424, so that the assemblage of the brushless motor is completed.
In the above related art actuator for the AFS, it has been proposed to form the casing and the gears of the gear mechanism, using a resin. However, the related has various problems and disadvantages. For example, but not by way of limitation, when the casing is molded of a glass fiber-containing PBT resin suited for casing, warp is liable to develop in this resin-molded casing. Therefore the distance between axes of adjacent gears of the contained gear mechanism varies, which invites problems such as inaccurate meshing of the gear train, the production of abnormal sounds and the development of a slip between the meshed gears, thus preventing the proper operation of the gear mechanism.
To prevent such warp of the casing, it may be proposed to form a rib (counter-rib) integrally on and along a peripheral edge portion of the casing, the rib projecting from an outer surface of the casing away from its adjacent bent portion. However, the counter-rib projects several millimeters from the outer surface of the casing, and therefore the outer size of the casing is increased by this rib. Further, this invites a problem in that the size of the actuator is increased, so that the ability of mounting the actuator within the lamp is lowered.
Further, in the related art, wear resistance of the meshed gears is secured by the grease applied to the gears to provide lubrication therebetween. However, when the actuator, mounted within the lamp, is heated by the lamp so that its temperature rises, the grease evaporates and is dissipated to the exterior of the casing. The dissipated grease deposits on a surface of lens of the lamp, and is solidified to fog the lens, thus inviting a so-called grease-fogging problem. Particularly in recent lamps, a transparent lens (outer cover) has been extensively used therefore, the fogging by the grease is a cause for deteriorating the quality of the lamp.
Further, in the related art brushless motor, the rotor 426 comprises the yoke 427, the rotor magnet 428, the bushing 4272, and the gear 441. therefore, the number of the component parts is relatively large. Further, when assembling the rotor 426, the bushing 4272 is press-fitted into the yoke 427 to be integrally connected thereto, and the rotation shaft 423 is passed through the bushing 4272 in a press-fitted condition. Further, the gear 441 is press-fitted on the rotation shaft 423 to be fixed thereto.
As a result, the operations using the press-fitting apparatus, are required, and much time and labor are required for the assembling operation, and the overall cost, including the cost of the parts and the cost of the motor-assembling operation, increases, and therefore it is difficult to achieve the low cost-design of the motor. In addition, press-fitting margins for the purpose of press-fitting the parts need to be provided on the rotation shaft 423 in the axial direction, and it is difficult to reduce the axial dimension of the rotation shaft.
Furthermore, the bushing 4272, the yoke 427 and the gear 441 are made of metallic materials, respectively, and this is a barrier to the lightweight design. Particularly, the yoke 427, made of metal, has an increased weight, and therefore an inertia moment of the rotor 426 is liable to become large, which causes the vibration of the rotor when it rotates at high speed. Furthermore, when the precision of assembling of the bushing 4272, yoke 427 and gear 441 relative to the rotation shaft 423 is low, the yoke 427 and the gear 441 fail to rotate in a common plane relative to the rotation shaft 423, and this causes the rotation balance to be disturbed, so that rotation characteristics are lowered.
Also, the related art brushless motor is of such a construction that the stator coil 424 is fitted on the outer periphery of the hollow boss 414. therefore, it is difficult to highly precisely set the stator coil 424 in its fitted position relative to the hollow boss 414 in both the circumferential direction and directions of this hollow boss. And besides, the stator coil 424, after being fitted on the hollow boss 414, is liable to be moved around the hollow boss 414 by vibrations and an impact. As a result of this movement, the stator coil 424 may be displaced out of position. Thus, misregistration may develop between the rotor 426 and the stator coil 424, and the intended magnetic force may fail to be produced between the stator coil 424 and the rotor magnet 428 of the rotor 426. The foregoing situation leads to a problem that the rotational force of the motor is lowered.
Furthermore, when mounting the stator coil 424 on the printed circuit board 45, the terminals 4243a of the coils 4243 are soldered to the electrodes on the printed circuit board. However, this operation is effected, utilizing a gap formed between the stator coil 424 and the printed circuit board 45, and therefore the soldering operation is difficult and requires meticulous attention.